Julie is a young Scottish aristocrat who works as a spy and translator for the British war effort. Currently held captive by the Nazis, she claims to be a coward and agrees to write down everything she knows about the British air force to avoid further torture. She is highly educated and fluent in French and German. She uses her sharp wit to cope with the terrible conditions of her imprisonment. Her detailed confession focuses heavily on her deep friendship with a pilot named Margaret Brodatt.

Margaret is a talented pilot from a working-class background, raised by her Russian-Jewish grandparents. She possesses a natural affinity for machines and navigation. After witnessing a plane crash, she pursues flight training and eventually joins the Air Transport Auxiliary to ferry aircraft for the war effort. Her calm demeanor and technical skill provide a steadying presence for Julie during their secret operations.

Captain Von Linden is a highly educated SS officer and former headmaster who runs the Gestapo headquarters in Ormaie. He strikes a terrifying balance between urbane courtesy and ruthless brutality. He regularly engages Julie in literary discussions about works like Goethe's Faust while simultaneously subjecting her to intense psychological pressure and the threat of execution. He is a methodical man who closely monitors the progress of Julie's written confession.

Jamie is Julie's younger brother and a dedicated pilot. After surviving a crash into the freezing North Sea early in the war, he loses two fingers on each hand and all of his toes. He continues to support the war effort despite these severe injuries. He shares his sister's quick wit and deep loyalty to their family.

Anna is a civilian German translator employed by the SS at the Ormaie headquarters. She is tasked with ensuring Julie stays on schedule with her written confession. She often carries out harsh administrative duties and strictly enforces the rules of the prison, though her background as a civilian sets her apart from the military officers.

Dympna is a confident civilian pilot whose emergency landing deeply impresses a young Margaret. She actively encourages Margaret's interest in aviation and promises to give her a ride once the plane is repaired. She later uses her connections to help Margaret enter the Women's Auxiliary Air Force.

Etienne is a French collaborator working for the Nazis in Ormaie. He actively participates in the oppression of his fellow citizens and assists the Gestapo in managing their prisoners. His presence creates an atmosphere of local betrayal within the prison walls.

Georgia is an American broadcast journalist known for creating radio programs sympathetic to Fascist causes. She arrives at the prison to conduct a propaganda interview, aiming to document the supposedly humane treatment of prisoners by the Nazis. Her presence introduces international media attention to Julie's isolated captivity.

Lady Esmé is Julie and Jamie's mother. She resides at Craig Castle, where she takes in refugee boys from Glasgow to protect them from the war. She maintains a loving, traditional household and symbolically leaves the windows open for her children's safe return.

Beryl is a young woman and friend of Margaret before the war intensifies. She is present when Dympna's plane crashes, rushing alongside Margaret to help pull the pilot from the wreckage.

Isolde is the teenage daughter of Captain Von Linden. She currently attends a boarding school in Switzerland, safely removed from the violence of the war her father actively orchestrates.

Nikolaus Ferber is a high-ranking Nazi official and Amadeus Von Linden's superior. He monitors the progress of the interrogations from afar and issues strict orders regarding the transfer of important prisoners to concentration camps.

An enigmatic civilian working for British intelligence who spots the potential in both Julie and Margaret. He tests their quick thinking and helps facilitate their entry into highly classified war operations.